The effect of the Mo/W ratio on the catalytic properties of alumina supported hydrotreating catalysts prepared from mixed SiMo6W6 and SiMo9W3 heteropolyacids

International audienceNew mixed H 4 [SiMo n W n-12 O 40 ] (n = 6 and 9) Keggin type heteropolyacids (HPAs) have been successfully synthesized, as confirmed by single-crystal XRD, Raman and IR spectroscopy analysis. The resulting polyoxometallates were used for preparation of hydrotreatment catalysts. Mo(W)/Al 2 O 3 catalysts were synthesized by incipient wetness impregnation of alumina support with water solutions of prepared mixed Keggin HPAs and corresponding counterparts based on mixture of monometallic H 4 [SiMo 12 O 40 ] and H 4 [SiW 12 O 40 ] HPAs. Oxidic catalysts were analyzed by Raman spectroscopy to determine the precursor structure after deposition. Catalysts in sulfided state were characterized by high-resolution transmission electron microscopy (HRTEM), high angle annular dark field imaging (HAADF) and X-ray photoelectron spectroscopy (XPS) and were tested in co-hydrotreating of dibenzothiophene (DBT) and naphthalene. The use of new mixed Keggin HPAs made it possible to obtain catalysts with mixed MoWS 2 active centers, which was confirmed by HAADF. Moreover, the Mo/(Mo + W) ratio has a direct effect on the structure of the active phase species. An ordered core-shell structure with Mo atoms in the core is maintained until the fraction of molybdenum in mixed MoW/Al 2 O 3 catalyst exceeds 50 %, where a more disordered structure is observed. Moreover, this Mo/(Mo + W) ratio of 0.5 is optimal to achieve a maximum catalytic activity. Indeed, the turnover frequencies (TOF) of the MoWS 2 edge centers with random atoms distribution in a cluster as in Mo 9 W 3 /Al 2 O 3 , was lower compared to that of Mo 6 W 6 /Al 2 O 3 with core-shell structure

Activity of mo(w)s-2/sba-15 catalysts synthesized from simow heteropoly acids in 4,6-dimethyldibenzothiophene hydrodesulfurization

International audienceMo(W)/SBA-15 catalysts are prepared using heteropoly acids H4SiMo12O40, H4SiW12O40, and H4SiMo3W9O40. The catalysts in the sulfide form are studied by low-temperature nitrogen adsorption, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Catalytic properties are tested in the hydrodesulfurization of 4,6-dimethyldibenzothiophene. It is shown that the gas-phase sulfiding of Mo(W)/SBA-15 catalysts leads to increase in the average length of particles and the number of Mo(W)S2 layers in active phase particles compared with liquid-phase sulfiding with the use of dimethyl sulfide. The replacement of a quarter of tungsten atoms with molybdenum ones makes it possible to considerably improve the catalytic activity of the mixed catalyst Mo + W/SBA-15 compared with the monometallic counterparts. This effect can be enhanced due to the use of mixed heteropoly acid H4SiMo3W9O40 as a precursor of the active phase of the MoW/SBA-15 catalyst, which is apparently associated with the formation of MoWS2 active sites

Bulk hydrotreating MonW12-nS2 catalysts based on SiMonW12-n heteropolyacids prepared by alumina elimination method

International audienceA series of unsupported mono- and bimetallic MonW12-nS2 catalysts were synthesized by alumina elimination from supported MonW12-nS2/Al2O3 samples using acid etching. Alumina supported catalysts have been in turn prepared by using monometallic H4SiMo12O40 and H4SiW12O40 heteropolyacids (HPAs), their mixture with Mo/W atomic ratio equal to 1/11 and 3/9, and mixed bimetallic H4SiMo1W11O40 and H4SiMo3W9O40 HPAs. All catalysts were characterized by N2 adsorption, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), extended X-ray absorption fine structure (EXAFS) spectroscopy and powder X-ray diffraction (XRD) and their performance were evaluated in simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydrogenation (HYD) of naphthalene. The etching process led to a successful removal of all the support and of the partially sulfided species, with sulfidation degrees of both Mo and W above 90 % on the final bulk solids. The active phase also underwent a rearrangement, as higher average length and stacking were measured on the bulk catalysts than on the original supported ones. Mixed MoWS2 phase was evidenced in all solids, prepared from mixed HPAs (MonW12-nS2) or from the mixture of monometallic HPAs (RefMonW12-nS2), by EXAFS and ToF-SIMS, with however a larger quantity on the MoW solids. It seems that the mixed MoWS2 phase observed on the supported MoW catalysts is maintained through the etching process, while on RefMonW12-nS2 the mixed phase, observed in a much lesser extent in the corresponding supported catalyst, could result from the aggregation of the monometallic slabs. MonW12-nS2 catalysts were found more effective than the monometallic catalysts and than the corresponding RefMonW12-nS2, in both dibenzothiophene hydrodesulfurization and naphthalene hydrogenation, which was related to the presence of the mixed phase maintained through the etching of the support